Microlocating lithium in the mouse embryo by use of a (n, α) nuclear reaction

Summary The quantitative imaging of lithium distribution, in histological sections of 15-days old mouse embryos (whose mother had been submitted to Li-treatment), was performed using⁶Li isotope as tracer,⁶Li(n,)³H nuclear reaction for detection, and dielectric track detectors. Despite the particular difficulties of cryosectioning the embryos without disturbing the lithium distribution, the Li regionalization appeared to be very clear-cut. The ectomesodermic tissues were significantly more loaded with lithium than the endodermic ones. This is probably related to the ectomesodermic tissues being also those most sensitive to the teratogenic effect of lithium. The Li-distribution in the embryo brain was almost homogeneous, instead of being heterogeneous as in adult brain. The mean Li-concentration in the embryo brain was not much below the Li concentration in the grey matter of the mother brain, but it was significantly larger than that in the white matter of the mother brain. Our results are discussed in the context of teratogenic effects observed in situ during mammalian development.     

Bufonid nucleocytoplasmic hybrids arrested at the early gastrula stage lack a fibronectin-containing fibrillar extracellular matrix

Summary Most hybrids betweenBufo bufo andB. calamita obtained by nuclear transplantation become arrested at the early gastrula stage. In both parental controls and the hybrid embryos, the presence and distribution of extracellular matrix was analysed with fluorescent wheat germ agglutinin and by immunolabelling with antibodies directed against fibronectin. InB. bufo andB. calamita gastrulae and in the few hybrids that complete gastrulation, the inner surface of the blastocoel roof is covered by a fibronectin-rich fibrillar matrix. In nucleocytoplasmic hybrids whose development was arrested at the gastrula stage, the fibronectin-containing extracellular matrix was either totally absent or poorly developed and disorganized.     

Experimentally induced true hermaphroditism in genetically female fowl

Summary Two types of hermaphroditism were experimentally induced in genetically female fowls by grafting of embryonic testes in embryos. Of the 27 hermaphrodites observed during the 8 months after hatching, 20 possessed a right testis and a left ovary and 7 a right testis and a left ovotestis. The testes and ovotestes contained seminiferous tubules with a more or less developed germ cell complement, attaining in many cases the early spermatid stage. The interstitial tissue was poorly functional, as shown by the absence of male secondary sex characters. The ovary or ovarian part of the ovotestes possessed numerous small ovarian follicles. The female arrangement of the plumage and the absence of spurs demonstrated the secretion of oestrogens. A mechanism is proposed for explaining this partial masculinization of genetically female gonads, a phenomenon which occurs during the period of embryonic sex differentiation, and is responsible for this experimental true hermaphroditism.     

Characterization of a new class of circular DNA molecules in yeast

This paper describes the isolation of a pure population of covalently closed circular twisted DNA molecules from yeast. These molecules are homogeneous in size, that is consist of monomers of 2.2μ and of multiple length oligomers of n x 2.2μ. While no data rule out the mitochondrial origin of this DNA, its actual intracellular localization remains unknown; it displays the same buoyant density as the main nuclear DNA and therefore is not the heavy nuclear satellite DNA (γ-DNA described by Moustacchi and Williamson (1966)); although circular molecules represent only 1 to 5 % of the total DNA, they can be prepared in sizable and reproducible amounts by a method based on the use of mechanical disruption of yeast cells rather than lysis by snail gut juice.     

Cellular Studies of X-Ray Induced Inhibition of Lens Regeneration

Whole-body X-irradiation of adult newts 0 to 3 days after lentectomy inhibits transformation of the dorsal iris epithelium into a lens in all cases. The first question raised was whether irradiation affects infiltration of the iris area by macrophages, and the phagocytic activities of these cell types in the iris epithelium (prominent phenomena in this system). The number of macrophages infiltrating into the iris epithelium, and their phagocytic activities (indicated by uptake of melanosomes) were not affected by irradiation under those conditions. The second group of experiments concerns the possible effects of irradiation on DNA replication of iris epithelial cells, which become transformed into lens cells in the non-irradiated system. Autoradiographic studies of iris epithelial cells in vivo revealed a significant suppressive effect of irradiation on the frequencies of cells incorporating ³H-thymidine 7 and 14 days after lentectomy. When autoradiography was applied to the primary pure culture of iris epithelial cells at different time intervals after the start of culture and irradiation in vitro , significant and persistent reduction of cell labelling due to irradiation, was demonstrated. Multiplication of spread cells in the iris epithelial culture was strongly and persistently inhibited throughout a period of 2 months. Inhibition of cell labelling and of cell multiplication was always accompanied by reduction in the extent of de-pigmentation of iris epithelial cells. De-pigmentation is one of the requirements for the cells become transformed into lens cells. The possible mechanism of radiation-induced inhibition of lens regeneration is discussed.     

Development of the pulmonary vasculature in newborn lambs: structure-function relationships

Our objectives were 1) to describe the quantitative light microscopy and ultrastructure of newborn lamb lungs and 2) to correlate hemodynamic changes during normoxia and hypoxia with the morphology. By light microscopy, we measured the percent muscle thickness (%MT) and peripheral muscularization of pulmonary arteries and veins from 25 lambs aged less than 24 h, 2-4 days, 2 wk, and 1 mo. At the same ages, lungs were isolated and perfused in situ and, after cyclooxygenase blockade with indomethacin, total, arterial (delta Pa), middle (delta Pm), and venous pressure gradients at inspired O2 fractions of 0.28 (mild hyperoxia) and 0.04 (hypoxia) were determined with inflow-outflow occlusion. During mild hyperoxia, delta Pa and delta Pm fell significantly between 2-4 days and 2 wk, whereas during hypoxia, only delta Pm fell. The %MT of all arteries (less than 50 to greater than 1,000 microns diam) decreased, and peripheral muscularization of less than 100-microns-diam arteries fell between less than 4 days and greater than 2 wk. Our data suggest that 1) the %MT of arteries determines normoxic pulmonary vascular resistance, because only arterial and middle segment resistance fell, 2) peripheral muscularization is a major determinant of hypoxic pulmonary vasoconstriction, because we observed a fall with age in peripheral muscularization of less than 100-micron-diam arteries and in delta Pm with hypoxia, and 3) the arterial limit of the middle segment defined by inflow-outflow occlusion lies in 100- to 1,000-microns-diam arteries.     

Modelling of the three-dimensional architecture of group I catalytic introns based on comparative sequence analysis

Alignment of the 87 available sequences of group I self-splicing introns reveals numerous instances of covariation between distant sites. Some of these covariations cannot be ascribed to historical coincidences or the known secondary structure of group I introns, and are, therefore, best explained as reflecting tertiary contacts. With the help of stereochemical modelling, we have taken advantage of these novel interactions to derive a three-dimensional model of the conserved core of group I introns. Two noteworthy features of that model are its extreme compactness and the fact that all of the most evolutionarily conserved residues happen to converge around the two helices that constitute the substrate of the core ribozyme and the site that binds the guanosine cofactor necessary for self-splicing. Specific functional implications are discussed, both with regard to the way the substrate helices are recognized by the core and possible rearrangements of the introns during the self-splicing process. Concerning potential long-range interactions, emphasis is put on the possible recognition of two consecutive purines in the minor groove of a helix by a GAAA or related terminal loop.